4-layer PCB ground connection

[Palpurul]

Hello,

I'm designing a 4-layer PCB and I finally finished routing, but I am kind of confused about a grounding of the last layer in my PCB.
I went with a very conventional stack-up:
1-layer - signal routing
2-layer - GND
3- layer - PWR
4- layer - signal routing (almost blank)
I almost only used the first three layers, 4th layer is almost blank. I am thinking about grounding it (of course). Should I connect this layer with all ground vias in my PCB (that's what I did with the second layer) or should I connect this layer to the ground with only one fat via?

Thanks!

 

[KlausST]

Hi,

A GND layer is best if there are no traces, just a solid copper plane. This I reccommend for your layer2.

For your layer4, I assume you speak about "copper pour" around the traces. In my eyes this is no GND plane useful fir nowadays high speed/high current applications.
I'm generally no friend of copper pour, not "just to fill the gaps" and much less as replacement for a true GND plane.

But other people use the copper pour.

So it's on your application and on your personal taste..whether to use copper pour or not

Klaus

 

[Palpurul]

I got solid copper plane in layer 2 as you said. As for my 4th layer (bottom layer). I got almost no trace. My question is should I just turn it to another another ground plane?

 

[senilicus]

That's all up to you. You can add a plane or add copper pour. Make sure that there is as much copper aspossible on the outer layers. This will help the plating en etching process.

 

[SLK001]

My philosophy of grounding is to flood every possible mm² with ground copper and then connect all the grounds with many thru-hole vias. This makes the impedance of the grounds as low as possible. If you have high current areas, isolate the ground return path with "herding" cuts in all the ground coming from that area to the main ground connection. A herding cut is simply a thin (~0.010") cut in the ground plane, creating a "star" grounding scheme. If you have multiple layers with ground, and you should, don't place the cuts right on top of each other, but stagger them by 0.050" or so.

 

[gopichand57]

Yes bro you copy the layer 2 as bot layer no worries....don't connect with one fat via....